The chromosome numbers of the endosperm and the embryo have been considered to play a vital role in proper endosperm development. However, various hypotheses suggested from time to time could not fully explain seed failure in terms of genome balance. The hypothesis that triploidy per se is an essential condition for normal endosperm development and that imbalances in chromosome number lead to anomalous development was tested in a study involving interploidy crosses in maize and the results confirm the validity of this hypothesis.
The 3n x 2n crosses were made to manipulate the chromosome number of the endosperm. The kernels obtained from these crosses were classified into eight categories on the basis of extent of kernel development. The plump kernels were classed in category I and completely shrivelled kernels in category VIII.
The chromosome counts in the root tip of the seedlings from kernels in various categories were used for extrapolation of the chromosome number of the endosperm. It was observed (Table 1) that the endosperm chromosome number in different categories ranged from 30 to 46. However, no kernel with 42 chromosomes in the endosperm was observed.
The highest mean number of chromosomes in the endosperm was 37.33 in category VIII (shrivelled kernels). The lowest mean number (31.29) was observed in category I (plumps). The progressive increase in kernel shrivelling from category I to VIII was observed to be correlated with the increase in mean chromosome number in the endosperm. No significant differences in mean chromosome number were observed among categories I, II, and III, and among categories IV, V, and VI. Accordingly, four groups differing significantly in the endosperm chromosome number could be identified. These four groups differed among themselves in the extent of endosperm development. These results suggest a positive correlation between the increasing endosperm chromosome number above 30 and the extent of kernel shrivelling.
D. S. Mathur and K. R. Sarkar
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